The pulse-reserve character of desert ecosystems presents particular challenges to sustainable resource management. While the notion of sustainability implies some sort of balance between resource provision and extraction, the extreme variability inherent in desert ecosystems tends towards boom-and-bust cycles rather than a steady flow of environmental goods and services. As a result, sustainability is difficult to define for desert ecosystems and certainly cannot be achieved by prescribing a fixed carrying capacity (such as, the number of livestock that a particular region can sustain; Behnke and Scoones 1993).

Mobile, extensive forms of grazing have been found to be well adapted to the variable resource availability in desert ecosystems (Niamir-Fuller 1999). Traditional users have learned to exploit ecosystem cycles sustainably, through mobility and regulation as a means to moderate rangeland use (as in the collective reserve Hema system in Arabia; see Chapter 2). In contrast, modern trends toward the sedentarization of pastoralists and the provision of subsidized supplemental animal feed, though implemented in the interest of economic sustainability, increase pressures on ecosystems by allowing for long periods of stay (Al-Rowaily 1999).

Sustainable resource management policies must respond to the pulse-reserve character of the desert ecosystem by supporting mobile or otherwise flexible systems, which can respond to the variable and unpredictable desert environment and still remain economically viable over long periods of time. This support can take the form of providing mobile services (medical care, schooling), encouraging risk spreading through common property management (Hesse and Trench 2000), and providing timely and accurate information about the state of pastures. Mitigating the "bust" part of the cycle is another important component of the sustainable management of desert ecosystems. This includes not only emergency support during drought crises, but also proactive management to increase human and societal resilience, by creating diverse rural income opportunities, providing support for animal marketing, providing credit, and establishing other forms of insurance that can sustain rural livelihoods during times of stress (Box 6.4). An alternative is to encourage urbanization that essentially removes pressures on rural natural resources (Portnov and Safriel 2004).